The present invention relates to a video image storage device, and more particularly to a video image storage device capable of memorizing digital signals obtained by converting input video signals into the digital signals by means of an A/D converter and capable of outputting the stored video signals in the device at the time when needed. The video image storage device can be used for signal sources from various kinds of image recording apparatus such as medical video imaging cameras, laser printers, thermal printers and ink jet printers, and also can be used for signal sources of files of the picture archiving and communication system (PACS) which is a simple diagnostic system including analog signal sources therein. Further, the video image storage device can be used as an image storage device for an X-ray television and cinematographic system, an image buffer and a scanning converter by way of its image memorizing function.
In a conventional manner, video signals having a certain line numbers/frame are stored in a frame memory of a storage device corresponding to the line numbers/frame by converting the video signals into digital signals. In case of interlace scanning, the term "frame" means a complete image consisting of two fields, and the term "frame memory" means a memory which can memorize images in the form of digital signals. The digital signals stored in the frame memory can be converted into analog video signals, when determined necessary, and also can be output in the form of analog video signals having the same scanning line numbers/frame as those of the input video signals. Accordingly, when the frame memory memorizes input video signals having the scanning line numbers/frame of 525 lines/frame, for example, the video signals having the same line numbers/frame are output. In the same manner, when the frame memory memorizes input video signals having the line numbers of 1024 lines/frame, the video signals having the same scanning line numbers as those of the input video signals are output from the frame memory. After the video images are stored in the frame memory, image processing such as magnification of screen images by adding raster lines between original raster lines or reduction of screen images by reducing original rester lines, or changes of aspect ratio of screen images can be made by use of a microcomputer installed outside the image storage device or a control circuit in the image storage device. Raster line erasure by adding raster lines between original raster lines can be made by use of the linear vertical shift method, the average vertical shift method and the like. Contrast control of the screen images can also be made when it is needed and thus, screen images having high definition can be obtained.
The aforementioned conventional video image storage devices are used for various types of diagnostic modalities having different scanning line numbers/frame to make video screen images. In general, scanning line numbers/frame are in the range from 500 to 2000 lines/frame. In such medical diagnostic modalities, CT, DF, US, RI, MRI and X-ray television by the use of image intensifier have been known. In recent years, computed radiographic (CR) system, which is one of the digital radiographic systems which has been developed. The CT stands for computer tomography which uses tomographic apparatus including a computer and can detect minute amount of differences among X-ray absorptive coefficients at each part of cross-sectional plan of human brain, for instance. The DF, US RI and MRI stand for digital fluorography, ultrasonography, radioisotopic imaging and magnetic resonance imaging, respectively.
In the above medical diagnostic modal systems, a plurality of image storage devices capable of storing video signals corresponding to scanning line numbers/frame intrinsic to the modality of diagnostic apparatus is needed for the purpose of memorizing the video signals from such apparatus. Therefore, for storing image signals, each diagnostic apparatus must have an independent video image storage device that causes increased cost and space for installation.